The chemical modification of surfaces to achieve desired chemical and/or physical characteristics has been previously described. For example, U.S. Pat. Nos. 4,722,906; 4,973,493; 4,979,959; 5,002,582; and 5,512,329 (each of which is commonly owned by the assignee of the invention described herein, and the disclosure of each is incorporated herein by reference), relate to surface modification by the use of latent reactive groups to achieve covalent coupling of reagents such as biomolecules and synthetic polymers to various substrates. The preferred latent reactive group is typically described as a photochemically reactive functional group (“photoreactive group”). When exposed to an appropriate energy source, a photoreactive group undergoes a transformation from an inactive state (i.e., ground state) to a reactive intermediate capable of forming covalent bonds with appropriate materials.
Such latent reactive groups can be used, for instance, to first derivatize a target molecule (e.g., thermochemically), in order to then photochemically attach the derivatized target molecule to a surface. Such a sequential approach is suitable in many situations, but can lack such attributes as speed, versatility, and ease of use, particularly when used with target molecules that are inherently difficult to first derivatize or under conditions that would result in loss of biological activity.
Latent reactive groups can also be used to prepare photoactivatable heterobifunctional molecules as linking agents, e.g., having a photoreactive group at one end or portion with a thermochemical attachment group at another (see, e.g., the above-captioned '582 patent, and U.S. Pat. No. 4,309,453, Reiner et al.). Such linking agents can be used to either attach nonreactive compounds to a surface or to prime a relatively inert surface in order to render it reactive upon exposure to suitable actinic radiation.
U.S. Pat. No. 5,414,075 (commonly owned by the assignee of the present invention and incorporated by reference herein), describes the use of linking agents to prime a surface to provide the surface with photoactivatable groups. This patent describes a restrained, multifunctional reagent useful for priming a support surface, or for simultaneous application with a target molecule to a support. Reagents such as those described above, including those described in the '075 patent, are generally hydrophobic. As a result, they are of relatively low solubility in aqueous systems, thereby often limiting their usefulness in hydrophilic applications.
U.S. Pat. No. 5,714,360, also commonly owned by the assignee of the invention herein described (and incorporated herein by reference), describes a chemical linking agent comprising a di-or higher functional photoactivatable charged compound. The linking agent provides at least one group that is charged under the conditions of use, in order to provide improved water solubility, and two or more photoactivatable groups in order to allow the agent to be used as a linking agent in aqueous systems. In a preferred embodiment, the charged groups include, but are not limited to, salts of organic acids (such as sulfonate, phosphonate, and carboxylate groups), onium compounds (such as quaternary ammonium, sulfonium, and phosphonium groups), and protonated amines, as well as combinations thereof. The photoreactive groups can be provided by two or more radicals of an aryl ketone such as benzophenone.
On a separate subject, common methods of attaching a polymer to a support surface include the attachment of a preformed polymer to a surface, and grafting a polymer to a surface. For instance, Tazuke et al. discuss the modification of polymer surfaces by the use of a grafting technique that involves treating a base polymer (e.g., polypropylene) with a reacting solution that contains sensitizers (e.g., benzophenone) and a selected polymer to be grafted onto the base polymer. “A Novel Modification of Polymer Surfaces by Photografting,” Tazuke et al., pp. 217–241, in Modification of Polymers, ACS Symposium Series 121 American Chemical Society, 1980.
On another subject, polymeric photosensitizers for initiating polymerization have been described. See, for instance, “Radical Polymerization,” C. H. Bamford, pp. 940–957 in Kroschwitz, ed., Concise Encyclopedia of Polymer Science and Engineering, 1990. In the subsection entitled “Photosensitized Initiation: Polymeric Photosensitizers and Photoinitiators,” the author states that “[p]olymeric photosensitizers and photoinitiators have been described. Many of these are polymers based on benzophenone, e.g., poly(p-divinylbenzophenone) (DVBP). Such rigid polymers are reported to be effective sensitizers since hydrogen abstraction from the backbone by excited benzophenone is less likely.” Further, U.S. Pat. No. 4,315,998 (Neckers) describes polymer-bound photosensitizing catalysts for use in the heterogeneous catalysis of photosensitized chemical reactions such as photo-oxidation, photodimerization, and photocycloaddition reactions. The polymer-bound photosensitizing catalysts are insoluble in water and common organic solvents, and therefore can be readily separated from the reaction medium and reaction products by simple filtration.
To the best of Applicants' knowledge, the art does not teach, nor are there commercial products that involve, the preparation or use of nonpolymeric coating agents that are themselves attached to a surface of an article in order to initiate photopolymerizaton from the surface. Nor are there generally reagents or methods that can be used to modify such surface properties as thickness, lubricity, and stability of coating in a controlled fashion. In contrast, there remains a need for coating agents having improved water solubility, and improved versatility in use. Finally, and in spite of the developments to date, there remains a need for reagents and methods that can be used to improve the initiation of photopolymerization to grow a polymer from a support surface.